Internet Engineering Task Force (IETF) C. Raiciu
Request for Comments: 6356 Univ. Politehnica of Bucharest
Category: Experimental M. Handly
ISSN: 2070-1721 D. Wischik
Univ. College London
October 2011
Coupled Congestion Control for Multipath Transport Protocols
Abstract
Often endpoints are connected by multiple paths, but communications
are usually restricted to a single path per connection. Resource
usage within the network would be more efficient were it possible for
these multiple paths to be used concurrently. Multipath TCP is a
proposal to achieve multipath transport in TCP.
New congestion control algorithms are needed for multipath transport
protocols such as Multipath TCP, as single path algorithms have a
series of issues in the multipath context. One of the prominent
problems is that running existing algorithms such as standard TCP
independently on each path would give the multipath flow more than
its fair share at a bottleneck link traversed by more than one of its
subflows. Further, it is desirable that a source with multiple paths
available will transfer more traffic using the least congested of the
paths, achieving a property called "resource pooling" where a bundle
of links effectively behaves like one shared link with bigger
capacity. This would increase the overall efficiency of the network
and also its robustness to failure.
This document presents a congestion control algorithm that couples
the congestion control algorithms running on different subflows by
linking their increase functions, and dynamically controls the
overall aggressiveness of the multipath flow. The result is a
practical algorithm that is fair to TCP at bottlenecks while moving
traffic away from congested links.
Raiciu, et al. Experimental [Page 1]RFC 6356 MPTCP Congestion Control October 2011Status of This Memo
This document is not an Internet Standards Track specification; it is
published for examination, experimental implementation, and
evaluation.
This document defines an Experimental Protocol for the Internet
community. This document is a product of the Internet Engineering
Task Force (IETF). It represents the consensus of the IETF
community. It has received public review and has been approved for
publication by the Internet Engineering Steering Group (IESG). Not
all documents approved by the IESG are a candidate for any level of
Internet Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6356.
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Table of Contents
1. Introduction ....................................................3
2. Requirements Language ...........................................5
3. Coupled Congestion Control Algorithm ............................5
4. Implementation Considerations ...................................7
4.1. Computing "alpha" in Practice ..............................7
4.2. Implementation Considerations when CWND is
Expressed in Packets .......................................8
5. Discussion ......................................................9
6. Security Considerations ........................................10
7. Acknowledgements ...............................................11
8. References .....................................................11
8.1. Normative References ......................................11
8.2. Informative References ....................................11
Raiciu, et al. Experimental [Page 2]RFC 6356 MPTCP Congestion Control October 2011